John Letts (1772-1851), the founding father of the Letts of London, and the eponymous diary, seems to have taken on the premises of James Asperne (1757-1820), bookseller and publisher of the 'The European Magazine' upon his death.

Letts had served an apprenticeship as a bookbinder, before setting up in business as a stationer in the City of London in 1796. From the Royal Exchange his clientele included "merchants and traders in the City. One of the chief requirements of the latter, apart from the regular recording of financial transactions, was a need to know about the movements of ships to and from the Port of London. This they obtained from a diary in which prominence was given to the working week, with a cash ruling through the diary section and tide tables in the opening pages.

Letts sensed that there could be a market for more general diaries of this type, but ones that were future-dated, so that the diary owner could plan ahead and not simply record the events of the day. His first such diary was issued in 1812 as a deliberately commercial product. Unlike existing diaries, it simply printed the dates of a six-day working week, Monday to Saturday, with no information other than the public holidays as they fell. The publication was branded by a printed label on the front cover 'Diary. 1812. Sold by John Letts Stationer. Royal Exchange'. There was soon a public demand for more informative contents, and by the early 1820s Letts was publishing a range of diaries in different sizes and formats, incorporating in their pages governmental, legal, commercial, and astronomical information, as what was essentially a combination of a detailed almanac and a day-to-day dated notebook" (Adrian Room for DNB).